A tenpin bowling ball may be of uniform, homogenous construction throughout, formed of hard rubber or of a variety of synthetic resins. More frequently, modern bowling balls are manufactured in a two-piece integrated construction comprising a spherical core with its exterior surface covered by a shell intended to afford optimal friction characteristics for the ball. In these balls, the overall weight of the ball is adjusted by varying the density and amount of fillers used in the rubber or resin of the core. An excellent bowling ball construction of this particular kind is described and claimed in Lee et al U.S. Pat. No. 4,461,478 issued July 24, 1984.
In a tenpin bowling ball, two or more frequently three finger holes are drilled into the ball to enable the bowler to lift and roll the ball. These finger holes result in an asymmetrical reduction in weight of the ball. To compensate for the resulting imbalance of the bowling ball, a variety of different expedients have been proposed. For example, Sauer U.S. Pat. No. 2,414,672 discloses an arrangement in which individual metal thimbles are mounted in the fingerholes; the thimbles include weights that compensate for the ball material removed from the fingerholes. Another previously known arrangement intended to compensate for the fingerhole weight imbalance is presented in Luth et al U.S. Pat. No. 2,291,738. The ball shown in the Luth et al patent incorporates an asymmetrical core, formed of two materials of quite different densities, with the heavier core material concentrated in the region around the fingerholes.
Another proposal for top-weighting of a bowling ball core to offset the loss of weight resulting from the drilling of fingerholes is presented in Randolph U.S. Pat. No. 3,865,369. This construction utilizes an asymmetreical core that is heavier or lighter than the body of the ball and is located closely adjacent to but entirely on one side of the mid-plane of the ball, the side where the fingerholes will be drilled. In one version the core constitutes a segment of a sphere; in others, it is of annular configuration. The spherical segment asymmetrical core is also disclosed in another Randolph U.S. Pat. No. 4,131,277. In the latter, there is also an illustration of a bowling ball having a bullet-shaped core.
These and most other prior art expedients are intended to compensate for the asymmetrical weight loss in a bowling ball that is occasioned by the drilling of one or more fingerholes into the ball. The intent is to afford rolling characteristics that most closely simulate those that would be obtained by a ball having a truly uniform weight distribution. For any such ball, of course, the "hooking" characteristic of the ball as it rolls down a lane, which is most desirable in achieving high scores, depends upon the frictional characteristics of the ball surface and the lane, the rotation imparted to the ball by the bowler, and other like factors. Even in those balls that include asymmetrical cores, such as those disclosed in the Luth et al and Randolph patents, the weight distribution within the ball does not contribute materially to an improvement in the hooking characteristic.
Another bowling ball construction, disclosed in MacDonald U.S. Pat. No. 4,268,034, includes two separate core members. One is a light weight core member aligned with a plane through the fingerhole axis of the ball. The other is an elongated top weight eccentrically disposed with respect to the finger holes. This arrangement is said to facilitate curving or hooking of the ball. An even more complex construction, employing a movable weight mounted on a lead screw extending into the interior of a blind hole in a bowling ball, is described in Skuse U.S. Pat. No. 3,591,177.